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Didemnum vexillum
Image courtesy of Ian Davidson, Smithsonian Environmental Research Center, Maryland, USA
Didemnum vexillum
Taxonomic Group: Tunicates


Didemnum vexillum is a rapidly spreading colonial tunicate that overgrows rocks, shellfish, and other organisms (e.g. sponges, hydroids, tunicates, algae). It probably originated from the Northwest Pacific, possibly Japan, but has been reported in several parts of the world including New Zealand, North America, and Europe. Its identification in these introduced areas had been debated, but recent genetic and morphological studies confirmed that many of these global populations are D. vexillum. Its first known occurrence on the East Coast of the US was in Damariscotta River estuary, Maine in 1982. It is now common from Shinnecock Inlet, New York to Eastport, Maine. The first occurrence of D. vexillum on the West Coast was in San Francisco Bay in 1993, but it can now be found from Bahia San Quintin, Mexico to Sitka, Alaska. Didemnum vexillum has the potential to cause significant economic damage to fisheries and aquaculture.  It can also have negative ecological impacts and in some areas its rapid expansion has reduced the abundance of previously established benthic species.

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Fofonoff PW, Ruiz GM, Steves B, Simkanin C, & Carlton JT (2018)
National Exotic Marine and Estuarine Species Information System.
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Marine Invasions Lab
Smithsonian Environmental Research Center

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Edgewater, MD 21037-0028 Tel: 443 482 2200
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